1. Field of the Invention
The present invention relates to a transparent heat-shielding member having a transparent screen function that enables an image projected onto a screen by a projector to be seen as a reflected image from the projector side and as a transmitted image from the opposite side of the projector across the screen, or in other words, enables the image to be clearly viewed from both sides by viewers, as well as the background to be transparently viewed.
2. Description of Related Art
From the viewpoint of preventing global warming and saving energy, in order to block heat rays (infrared rays) from sunlight entering through the windows of buildings, display windows of shops, the windows of vehicles and the like, a transparent heat ray blocking member is commonly provided on or within a window pane or an organic transparent substrate, thereby to reduce the temperature inside the room or vehicle (for example, Patent Document 1 listed below). In addition, recently, from the viewpoint of saving energy throughout the year, transparent heat-shielding/heat-insulating members having not only heat shielding properties that block heat rays that cause a temperature increase in summer, but also heat-insulating properties that suppress the escape of heat from the inside of the room in winter by shielding far infrared rays emitted from the inside to the outside of the room through a light transmitting member (reflecting far infrared rays toward the inside of the room) so as to reduce the heating load have been proposed as solar control films and are increasingly introduced into the market (for example, Patent Documents 2 to 4 listed below).
In recent years, attention has been focused on so-called “digital signage” used as a medium for providing advertisements, guidance and information, instead of conventional signboards, posters and large screen displays, in particular, in glass-walled commercial establishments, and display windows of convenience stores, department stores, and shops such as clothes and automobile shops by attaching a transparent screen onto a window or a display window so as to allow the window itself to function as a large screen, and projecting and displaying various content images such as advertisements, merchandise information and other information by using a projector from the inside while the transparent viewability is maintained at a level at which the interior state and goods can be viewed from the outside, because the digital signage has a very high eye-catching effect for people who are outside, is easily adapted to changes in the content, and is convenient. Likewise, in automobiles, attention has been focused on a head-up display (HUD) apparatus that projects and displays navigation information from a small-sized projector by using a portion of the surface of the windshield, a transparent or semi-transparent beam splitter, called a combiner, provided near the rearview mirror or near the driver's sight lines, or the like, or that projects and displays navigation information as a virtual image through the windshield, so as to allow the driver to see the navigation information without significantly moving his/her viewing point (for example, Patent Documents 5 to 8 listed below).
Patent Document 1: Japanese Patent No. 4190657
Patent Document 2: JP 2013-010341 A
Patent Document 3: JP 2013-151103 A
Patent Document 4: WO 2012/096304
Patent Document 5: Japanese Patent No. 3993980
Patent Document 6: JP 2013-210454A
Patent Document 7: Japanese Patent No. 4822104
Patent Document 8: JP 2011-113068 A
The heat-shielding members of Patent Documents 1 to 4 can, by being attached to a window, provide a heat-shielding function or a heat-shielding/heat-insulating function to the window itself, but they hardly function as a transparent screen for digital signage because they are not provided with a transparent screen function that displays content projected by a projector, and a design that gives consideration thereto is not disclosed.
To be specific, Patent Document 1 discloses an infrared shielding film obtained by coating a PET film with an infrared shielding layer made of an ionizing radiation curable resin in which a rare-earth metal-based infrared shielding agent is dispersed. The infrared shielding film shields near infrared rays through absorption, but it does not have a heat-insulating function that reflects far infrared rays. In addition, as far as it is understood from the reference examples and examples of the patent document, the infrared shielding film has a haze value as small as about 1%. Accordingly, at least an element for sufficiently scattering light is not included in the constituent members, and a design that gives consideration thereto is not disclosed, and thus the infrared shielding film hardly functions as a transparent screen for digital signage.
Patent Document 2 discloses a heat ray reflective film obtained by forming a heat ray reflective layer composed of a thin metal oxide film, a thin metal film and a thin metal oxide film onto a PET film by a sputtering method, and attaching a polyolefin resin film such as an OPP or COP coated with a hardcoat layer onto the heat ray reflective layer via an adhesive layer. However, the zeonor film used in an example has a haze value as small as 0.1%, and the haze value of the OPP films used in other examples is not clearly disclosed, but commercially available OPP films for use as a protective layer for a transparent heat ray reflective film have a haze value of 3% at the highest. Accordingly, at least an element for sufficiently scattering light is not included in the constituent members, and a design that gives consideration thereto is not disclosed, and thus the heat ray reflective film hardly functions as a transparent screen for digital signage.
Patent Document 3 discloses a transparent stacked film obtained by forming a transparent stacked portion in which a thin metal oxide film and a thin metal film are alternately stacked onto a PET film by a sol-gel method and a sputtering method, attaching an olefin resin film such as an OPP film onto the transparent stacked portion via an adhesive layer, and further coating the olefin resin film with a protective layer made of silicon oxide. However, the OPP films used in the examples have a haze value as small as 2%. Accordingly, at least an element for sufficiently scattering light is not included in the constituent members, and a design that gives consideration thereto is not disclosed, and thus the transparent stacked film hardly functions as a transparent screen for digital signage.
Patent Document 4 discloses a far infrared reflective stacked body obtained by forming, onto a PET film, a far infrared reflective layer composed of a single metal layer containing silver (Ag) in an amount of 95 to 100 mass % or a plurality of layers including a metal layer containing silver (Ag) in an amount of 95 to 100 mass %, a metal oxide layer and/or a metal nitride layer by a sputtering method, and coating the far infrared reflective layer with a hardcoat layer having one or more polar groups selected from the group consisting of a phosphoric acid group, a sulfonic acid group and an amide group. However, at least an element for sufficiently scattering light is not included in the constituent members, and a design that gives consideration thereto is not disclosed, and thus the far infrared reflective stacked body hardly functions as a transparent screen for digital signage.
On the other hand, the transparent screen members disclosed in Patent Documents 5 to 8 can provide, by being attached to a window, a transparent screen function that displays content projected by a projector on the window itself, but they are not provided with a near infrared ray shielding function or a far infrared ray reflecting function. In addition, a design that gives consideration thereto is not disclosed, and thus the transparent screen members hardly function as a transparent heat-shielding member or a transparent heat-shielding/heat-insulating member.
To be specific, Patent Document 5 discloses a transmissive screen obtained by coating a glass or PET film with a resin such as polyvinyl butyral resin, polystyrene resin, polyester resin, polyurethane adhesive or ultraviolet curable acrylate resin in which light diffusing particles such as acrylic resin particles, silicone resin particles or polystyrene resin particles are dispersed. However, none of the materials shields near infrared rays nor reflects far infrared rays. In addition, a design that gives consideration thereto is not disclosed, and thus the transmissive screen hardly functions as a transparent heat-shielding member or a transparent heat-shielding/heat-insulating member.
Patent Document 6 discloses a transmissive screen obtained by coating a PET film with a hydrophilic resin such as a completely or partially saponified polyvinyl alcohol or a cationically modified polyvinyl alcohol in which light diffusing particles made of, for example, amorphous synthetic silica, alumina or hydrated alumina are dispersed. However, none of the materials shields near infrared rays nor reflects far infrared rays. In addition, a design that gives consideration thereto is not disclosed, and thus the transmissive screen hardly functions as a transparent heat-shielding member or a transparent heat-shielding/heat-insulating member.
Patent Document 7 discloses a projection screen obtained by attaching, to both surfaces of a glass sheet, a PET film coated with a polarization-selective reflective layer made of a cholesteric liquid crystal resin having a selective reflection center wavelength in the visible light region and a PET film in which a transmissive volume hologram has been recorded and fixed by application of a hologram photosensitive material made of a photo polymer or the like and exposure to light, by using a pressure-sensitive adhesive. However, as long as the scope of the disclosure of Patent Document 7 is considered, none of the materials shields near infrared rays nor reflects far infrared rays. In addition, a design that gives consideration thereto is not disclosed, and thus the projection screen hardly functions as a transparent heat-shielding member or a transparent heat-shielding/heat-insulating member.
Patent Document 8 discloses a transmissive screen obtained by coating a glass sheet with a polyvinyl acetal resin in which nanodiamond particles having a very high refractive index are dispersed as light diffusing particles, or by forming them into a laminated glass. However, none of the materials shields near infrared rays nor reflects far infrared rays. In addition, a design that gives consideration thereto is not disclosed, and thus the transmissive screen hardly functions as a transparent heat-shielding member or a transparent heat-shielding/heat-insulating member.
As described above, despite the fact that a large number of windows in the surrounding living space are required to have a heat-shielding function or a heat-shielding/heat-insulating function as described above from the viewpoint of saving energy or to have a transparent screen function as described above from the viewpoint of digital signage, surprisingly, to the best of the inventors' knowledge, a member that has both functions has not been found, and an idea of providing such a member has not been conceived yet.
Furthermore, recently, it is taken for granted that a transparent screen for window display is required to have a high viewability that enables a content image projected by a projector to be viewed from a wide range of angles so as to maximize the function as digital signage. In addition thereto, opportunities are gradually increasing not only for a content image to be viewed from outside of the window to which the transparent screen has been attached (from the opposite side of the projector across the screen) as a transmitted image, but also for the content image projected onto the transparent screen to be viewed from inside of the window (from the projector side with respect to the screen) as a reflected image, and therefore there is an increasing need for a transmissive screen having excellent viewability from the inside and outside of the window, or in other words, excellent viewability from both sides of the screen. However, commercially available transmissive transparent screens have high forward light scattering properties and thus can provide a clear transmitted image as viewed from the opposite side of the projector across the screen, but the backward light scattering properties are not so high, and thus although it is possible to view the reflected image from the projector side, the image has a low brightness (luminance) and blurred. Accordingly, it cannot be said that the image clarity is sufficient.